Intracellular recordings will be made from parvocellular neurons in the hypothalamic slice preparation of the female guinea pig in order to elucidate the actions of 17 Beta-estradiol (E2) on luteinizing hormone-releasing hormone (LRH) neurons. Recent findings using this preparation have established that E2 can rapidly but reversibly polarize the membrane of arcuateventromedial (ARC-VM) neurons. This hyperpolarization was accompanied by a decrease in the input resistance, which would indicate that C1- and/or K+ are involved. The first phase of experimentation of the present proposal will address the mechanisms of action of E2 at the membrane level. Initial experiments will be conducted to block pre-synaptic activity and to measure the post-synaptic effects of E2. The question of what specific ions are involved in the conductance change will be investigated. The second phase of experimentation will entail identifying if the presumed receptor is membrane bound or cytoplasmic. The effects of estrogen antagonists on estrogen-mediated changes in excitability will also be studied. The morphological characteristics of these estrogen-sensitive neurons will be delineated through the intracellular injection of procion yellow. Finally, the changes in the LRH output of an individual slice will be measured during its exppsure to E2 in the medium by assaying (radioimmunoassay) the LRH in the effluent medium, the peptide constituents of the parvocellular neurons will be identified by immunocytochemistry.